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TailRecursionElimination.cpp
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1 //===- TailRecursionElimination.cpp - Eliminate Tail Calls ----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file transforms calls of the current function (self recursion) followed
10 // by a return instruction with a branch to the entry of the function, creating
11 // a loop. This pass also implements the following extensions to the basic
12 // algorithm:
13 //
14 // 1. Trivial instructions between the call and return do not prevent the
15 // transformation from taking place, though currently the analysis cannot
16 // support moving any really useful instructions (only dead ones).
17 // 2. This pass transforms functions that are prevented from being tail
18 // recursive by an associative and commutative expression to use an
19 // accumulator variable, thus compiling the typical naive factorial or
20 // 'fib' implementation into efficient code.
21 // 3. TRE is performed if the function returns void, if the return
22 // returns the result returned by the call, or if the function returns a
23 // run-time constant on all exits from the function. It is possible, though
24 // unlikely, that the return returns something else (like constant 0), and
25 // can still be TRE'd. It can be TRE'd if ALL OTHER return instructions in
26 // the function return the exact same value.
27 // 4. If it can prove that callees do not access their caller stack frame,
28 // they are marked as eligible for tail call elimination (by the code
29 // generator).
30 //
31 // There are several improvements that could be made:
32 //
33 // 1. If the function has any alloca instructions, these instructions will be
34 // moved out of the entry block of the function, causing them to be
35 // evaluated each time through the tail recursion. Safely keeping allocas
36 // in the entry block requires analysis to proves that the tail-called
37 // function does not read or write the stack object.
38 // 2. Tail recursion is only performed if the call immediately precedes the
39 // return instruction. It's possible that there could be a jump between
40 // the call and the return.
41 // 3. There can be intervening operations between the call and the return that
42 // prevent the TRE from occurring. For example, there could be GEP's and
43 // stores to memory that will not be read or written by the call. This
44 // requires some substantial analysis (such as with DSA) to prove safe to
45 // move ahead of the call, but doing so could allow many more TREs to be
46 // performed, for example in TreeAdd/TreeAlloc from the treeadd benchmark.
47 // 4. The algorithm we use to detect if callees access their caller stack
48 // frames is very primitive.
49 //
50 //===----------------------------------------------------------------------===//
51 
53 #include "llvm/ADT/STLExtras.h"
54 #include "llvm/ADT/SmallPtrSet.h"
55 #include "llvm/ADT/Statistic.h"
59 #include "llvm/Analysis/Loads.h"
64 #include "llvm/IR/CFG.h"
65 #include "llvm/IR/Constants.h"
66 #include "llvm/IR/DataLayout.h"
67 #include "llvm/IR/DerivedTypes.h"
68 #include "llvm/IR/DiagnosticInfo.h"
69 #include "llvm/IR/Dominators.h"
70 #include "llvm/IR/Function.h"
71 #include "llvm/IR/IRBuilder.h"
72 #include "llvm/IR/InstIterator.h"
73 #include "llvm/IR/Instructions.h"
74 #include "llvm/IR/IntrinsicInst.h"
75 #include "llvm/IR/Module.h"
76 #include "llvm/InitializePasses.h"
77 #include "llvm/Pass.h"
78 #include "llvm/Support/Debug.h"
80 #include "llvm/Transforms/Scalar.h"
82 using namespace llvm;
83 
84 #define DEBUG_TYPE "tailcallelim"
85 
86 STATISTIC(NumEliminated, "Number of tail calls removed");
87 STATISTIC(NumRetDuped, "Number of return duplicated");
88 STATISTIC(NumAccumAdded, "Number of accumulators introduced");
89 
90 /// Scan the specified function for alloca instructions.
91 /// If it contains any dynamic allocas, returns false.
92 static bool canTRE(Function &F) {
93  // TODO: We don't do TRE if dynamic allocas are used.
94  // Dynamic allocas allocate stack space which should be
95  // deallocated before new iteration started. That is
96  // currently not implemented.
97  return llvm::all_of(instructions(F), [](Instruction &I) {
98  auto *AI = dyn_cast<AllocaInst>(&I);
99  return !AI || AI->isStaticAlloca();
100  });
101 }
102 
103 namespace {
104 struct AllocaDerivedValueTracker {
105  // Start at a root value and walk its use-def chain to mark calls that use the
106  // value or a derived value in AllocaUsers, and places where it may escape in
107  // EscapePoints.
108  void walk(Value *Root) {
109  SmallVector<Use *, 32> Worklist;
110  SmallPtrSet<Use *, 32> Visited;
111 
112  auto AddUsesToWorklist = [&](Value *V) {
113  for (auto &U : V->uses()) {
114  if (!Visited.insert(&U).second)
115  continue;
116  Worklist.push_back(&U);
117  }
118  };
119 
120  AddUsesToWorklist(Root);
121 
122  while (!Worklist.empty()) {
123  Use *U = Worklist.pop_back_val();
124  Instruction *I = cast<Instruction>(U->getUser());
125 
126  switch (I->getOpcode()) {
127  case Instruction::Call:
128  case Instruction::Invoke: {
129  auto &CB = cast<CallBase>(*I);
130  // If the alloca-derived argument is passed byval it is not an escape
131  // point, or a use of an alloca. Calling with byval copies the contents
132  // of the alloca into argument registers or stack slots, which exist
133  // beyond the lifetime of the current frame.
134  if (CB.isArgOperand(U) && CB.isByValArgument(CB.getArgOperandNo(U)))
135  continue;
136  bool IsNocapture =
137  CB.isDataOperand(U) && CB.doesNotCapture(CB.getDataOperandNo(U));
138  callUsesLocalStack(CB, IsNocapture);
139  if (IsNocapture) {
140  // If the alloca-derived argument is passed in as nocapture, then it
141  // can't propagate to the call's return. That would be capturing.
142  continue;
143  }
144  break;
145  }
146  case Instruction::Load: {
147  // The result of a load is not alloca-derived (unless an alloca has
148  // otherwise escaped, but this is a local analysis).
149  continue;
150  }
151  case Instruction::Store: {
152  if (U->getOperandNo() == 0)
153  EscapePoints.insert(I);
154  continue; // Stores have no users to analyze.
155  }
156  case Instruction::BitCast:
157  case Instruction::GetElementPtr:
158  case Instruction::PHI:
159  case Instruction::Select:
160  case Instruction::AddrSpaceCast:
161  break;
162  default:
163  EscapePoints.insert(I);
164  break;
165  }
166 
167  AddUsesToWorklist(I);
168  }
169  }
170 
171  void callUsesLocalStack(CallBase &CB, bool IsNocapture) {
172  // Add it to the list of alloca users.
173  AllocaUsers.insert(&CB);
174 
175  // If it's nocapture then it can't capture this alloca.
176  if (IsNocapture)
177  return;
178 
179  // If it can write to memory, it can leak the alloca value.
180  if (!CB.onlyReadsMemory())
181  EscapePoints.insert(&CB);
182  }
183 
184  SmallPtrSet<Instruction *, 32> AllocaUsers;
185  SmallPtrSet<Instruction *, 32> EscapePoints;
186 };
187 }
188 
190  if (F.callsFunctionThatReturnsTwice())
191  return false;
192 
193  // The local stack holds all alloca instructions and all byval arguments.
194  AllocaDerivedValueTracker Tracker;
195  for (Argument &Arg : F.args()) {
196  if (Arg.hasByValAttr())
197  Tracker.walk(&Arg);
198  }
199  for (auto &BB : F) {
200  for (auto &I : BB)
201  if (AllocaInst *AI = dyn_cast<AllocaInst>(&I))
202  Tracker.walk(AI);
203  }
204 
205  bool Modified = false;
206 
207  // Track whether a block is reachable after an alloca has escaped. Blocks that
208  // contain the escaping instruction will be marked as being visited without an
209  // escaped alloca, since that is how the block began.
210  enum VisitType {
211  UNVISITED,
212  UNESCAPED,
213  ESCAPED
214  };
216 
217  // We propagate the fact that an alloca has escaped from block to successor.
218  // Visit the blocks that are propagating the escapedness first. To do this, we
219  // maintain two worklists.
220  SmallVector<BasicBlock *, 32> WorklistUnescaped, WorklistEscaped;
221 
222  // We may enter a block and visit it thinking that no alloca has escaped yet,
223  // then see an escape point and go back around a loop edge and come back to
224  // the same block twice. Because of this, we defer setting tail on calls when
225  // we first encounter them in a block. Every entry in this list does not
226  // statically use an alloca via use-def chain analysis, but may find an alloca
227  // through other means if the block turns out to be reachable after an escape
228  // point.
229  SmallVector<CallInst *, 32> DeferredTails;
230 
231  BasicBlock *BB = &F.getEntryBlock();
232  VisitType Escaped = UNESCAPED;
233  do {
234  for (auto &I : *BB) {
235  if (Tracker.EscapePoints.count(&I))
236  Escaped = ESCAPED;
237 
238  CallInst *CI = dyn_cast<CallInst>(&I);
239  // A PseudoProbeInst has the IntrInaccessibleMemOnly tag hence it is
240  // considered accessing memory and will be marked as a tail call if we
241  // don't bail out here.
242  if (!CI || CI->isTailCall() || isa<DbgInfoIntrinsic>(&I) ||
243  isa<PseudoProbeInst>(&I))
244  continue;
245 
246  // Special-case operand bundles "clang.arc.attachedcall" and "ptrauth".
247  bool IsNoTail =
250 
251  if (!IsNoTail && CI->doesNotAccessMemory()) {
252  // A call to a readnone function whose arguments are all things computed
253  // outside this function can be marked tail. Even if you stored the
254  // alloca address into a global, a readnone function can't load the
255  // global anyhow.
256  //
257  // Note that this runs whether we know an alloca has escaped or not. If
258  // it has, then we can't trust Tracker.AllocaUsers to be accurate.
259  bool SafeToTail = true;
260  for (auto &Arg : CI->args()) {
261  if (isa<Constant>(Arg.getUser()))
262  continue;
263  if (Argument *A = dyn_cast<Argument>(Arg.getUser()))
264  if (!A->hasByValAttr())
265  continue;
266  SafeToTail = false;
267  break;
268  }
269  if (SafeToTail) {
270  using namespace ore;
271  ORE->emit([&]() {
272  return OptimizationRemark(DEBUG_TYPE, "tailcall-readnone", CI)
273  << "marked as tail call candidate (readnone)";
274  });
275  CI->setTailCall();
276  Modified = true;
277  continue;
278  }
279  }
280 
281  if (!IsNoTail && Escaped == UNESCAPED && !Tracker.AllocaUsers.count(CI))
282  DeferredTails.push_back(CI);
283  }
284 
285  for (auto *SuccBB : successors(BB)) {
286  auto &State = Visited[SuccBB];
287  if (State < Escaped) {
288  State = Escaped;
289  if (State == ESCAPED)
290  WorklistEscaped.push_back(SuccBB);
291  else
292  WorklistUnescaped.push_back(SuccBB);
293  }
294  }
295 
296  if (!WorklistEscaped.empty()) {
297  BB = WorklistEscaped.pop_back_val();
298  Escaped = ESCAPED;
299  } else {
300  BB = nullptr;
301  while (!WorklistUnescaped.empty()) {
302  auto *NextBB = WorklistUnescaped.pop_back_val();
303  if (Visited[NextBB] == UNESCAPED) {
304  BB = NextBB;
305  Escaped = UNESCAPED;
306  break;
307  }
308  }
309  }
310  } while (BB);
311 
312  for (CallInst *CI : DeferredTails) {
313  if (Visited[CI->getParent()] != ESCAPED) {
314  // If the escape point was part way through the block, calls after the
315  // escape point wouldn't have been put into DeferredTails.
316  LLVM_DEBUG(dbgs() << "Marked as tail call candidate: " << *CI << "\n");
317  CI->setTailCall();
318  Modified = true;
319  }
320  }
321 
322  return Modified;
323 }
324 
325 /// Return true if it is safe to move the specified
326 /// instruction from after the call to before the call, assuming that all
327 /// instructions between the call and this instruction are movable.
328 ///
330  if (isa<DbgInfoIntrinsic>(I))
331  return true;
332 
333  if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
334  if (II->getIntrinsicID() == Intrinsic::lifetime_end &&
335  llvm::findAllocaForValue(II->getArgOperand(1)))
336  return true;
337 
338  // FIXME: We can move load/store/call/free instructions above the call if the
339  // call does not mod/ref the memory location being processed.
340  if (I->mayHaveSideEffects()) // This also handles volatile loads.
341  return false;
342 
343  if (LoadInst *L = dyn_cast<LoadInst>(I)) {
344  // Loads may always be moved above calls without side effects.
345  if (CI->mayHaveSideEffects()) {
346  // Non-volatile loads may be moved above a call with side effects if it
347  // does not write to memory and the load provably won't trap.
348  // Writes to memory only matter if they may alias the pointer
349  // being loaded from.
350  const DataLayout &DL = L->getModule()->getDataLayout();
351  if (isModSet(AA->getModRefInfo(CI, MemoryLocation::get(L))) ||
352  !isSafeToLoadUnconditionally(L->getPointerOperand(), L->getType(),
353  L->getAlign(), DL, L))
354  return false;
355  }
356  }
357 
358  // Otherwise, if this is a side-effect free instruction, check to make sure
359  // that it does not use the return value of the call. If it doesn't use the
360  // return value of the call, it must only use things that are defined before
361  // the call, or movable instructions between the call and the instruction
362  // itself.
363  return !is_contained(I->operands(), CI);
364 }
365 
367  if (!I->isAssociative() || !I->isCommutative())
368  return false;
369 
370  assert(I->getNumOperands() == 2 &&
371  "Associative/commutative operations should have 2 args!");
372 
373  // Exactly one operand should be the result of the call instruction.
374  if ((I->getOperand(0) == CI && I->getOperand(1) == CI) ||
375  (I->getOperand(0) != CI && I->getOperand(1) != CI))
376  return false;
377 
378  // The only user of this instruction we allow is a single return instruction.
379  if (!I->hasOneUse() || !isa<ReturnInst>(I->user_back()))
380  return false;
381 
382  return true;
383 }
384 
386  while (isa<DbgInfoIntrinsic>(I))
387  ++I;
388  return &*I;
389 }
390 
391 namespace {
392 class TailRecursionEliminator {
393  Function &F;
394  const TargetTransformInfo *TTI;
395  AliasAnalysis *AA;
397  DomTreeUpdater &DTU;
398 
399  // The below are shared state we want to have available when eliminating any
400  // calls in the function. There values should be populated by
401  // createTailRecurseLoopHeader the first time we find a call we can eliminate.
402  BasicBlock *HeaderBB = nullptr;
403  SmallVector<PHINode *, 8> ArgumentPHIs;
404 
405  // PHI node to store our return value.
406  PHINode *RetPN = nullptr;
407 
408  // i1 PHI node to track if we have a valid return value stored in RetPN.
409  PHINode *RetKnownPN = nullptr;
410 
411  // Vector of select instructions we insereted. These selects use RetKnownPN
412  // to either propagate RetPN or select a new return value.
413  SmallVector<SelectInst *, 8> RetSelects;
414 
415  // The below are shared state needed when performing accumulator recursion.
416  // There values should be populated by insertAccumulator the first time we
417  // find an elimination that requires an accumulator.
418 
419  // PHI node to store our current accumulated value.
420  PHINode *AccPN = nullptr;
421 
422  // The instruction doing the accumulating.
423  Instruction *AccumulatorRecursionInstr = nullptr;
424 
425  TailRecursionEliminator(Function &F, const TargetTransformInfo *TTI,
427  DomTreeUpdater &DTU)
428  : F(F), TTI(TTI), AA(AA), ORE(ORE), DTU(DTU) {}
429 
430  CallInst *findTRECandidate(BasicBlock *BB);
431 
432  void createTailRecurseLoopHeader(CallInst *CI);
433 
434  void insertAccumulator(Instruction *AccRecInstr);
435 
436  bool eliminateCall(CallInst *CI);
437 
438  void cleanupAndFinalize();
439 
440  bool processBlock(BasicBlock &BB);
441 
442  void copyByValueOperandIntoLocalTemp(CallInst *CI, int OpndIdx);
443 
444  void copyLocalTempOfByValueOperandIntoArguments(CallInst *CI, int OpndIdx);
445 
446 public:
447  static bool eliminate(Function &F, const TargetTransformInfo *TTI,
449  DomTreeUpdater &DTU);
450 };
451 } // namespace
452 
453 CallInst *TailRecursionEliminator::findTRECandidate(BasicBlock *BB) {
454  Instruction *TI = BB->getTerminator();
455 
456  if (&BB->front() == TI) // Make sure there is something before the terminator.
457  return nullptr;
458 
459  // Scan backwards from the return, checking to see if there is a tail call in
460  // this block. If so, set CI to it.
461  CallInst *CI = nullptr;
462  BasicBlock::iterator BBI(TI);
463  while (true) {
464  CI = dyn_cast<CallInst>(BBI);
465  if (CI && CI->getCalledFunction() == &F)
466  break;
467 
468  if (BBI == BB->begin())
469  return nullptr; // Didn't find a potential tail call.
470  --BBI;
471  }
472 
473  assert((!CI->isTailCall() || !CI->isNoTailCall()) &&
474  "Incompatible call site attributes(Tail,NoTail)");
475  if (!CI->isTailCall())
476  return nullptr;
477 
478  // As a special case, detect code like this:
479  // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call
480  // and disable this xform in this case, because the code generator will
481  // lower the call to fabs into inline code.
482  if (BB == &F.getEntryBlock() &&
483  firstNonDbg(BB->front().getIterator()) == CI &&
484  firstNonDbg(std::next(BB->begin())) == TI && CI->getCalledFunction() &&
486  // A single-block function with just a call and a return. Check that
487  // the arguments match.
488  auto I = CI->arg_begin(), E = CI->arg_end();
489  Function::arg_iterator FI = F.arg_begin(), FE = F.arg_end();
490  for (; I != E && FI != FE; ++I, ++FI)
491  if (*I != &*FI) break;
492  if (I == E && FI == FE)
493  return nullptr;
494  }
495 
496  return CI;
497 }
498 
499 void TailRecursionEliminator::createTailRecurseLoopHeader(CallInst *CI) {
500  HeaderBB = &F.getEntryBlock();
501  BasicBlock *NewEntry = BasicBlock::Create(F.getContext(), "", &F, HeaderBB);
502  NewEntry->takeName(HeaderBB);
503  HeaderBB->setName("tailrecurse");
504  BranchInst *BI = BranchInst::Create(HeaderBB, NewEntry);
505  BI->setDebugLoc(CI->getDebugLoc());
506 
507  // Move all fixed sized allocas from HeaderBB to NewEntry.
508  for (BasicBlock::iterator OEBI = HeaderBB->begin(), E = HeaderBB->end(),
509  NEBI = NewEntry->begin();
510  OEBI != E;)
511  if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++))
512  if (isa<ConstantInt>(AI->getArraySize()))
513  AI->moveBefore(&*NEBI);
514 
515  // Now that we have created a new block, which jumps to the entry
516  // block, insert a PHI node for each argument of the function.
517  // For now, we initialize each PHI to only have the real arguments
518  // which are passed in.
519  Instruction *InsertPos = &HeaderBB->front();
520  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) {
521  PHINode *PN =
522  PHINode::Create(I->getType(), 2, I->getName() + ".tr", InsertPos);
523  I->replaceAllUsesWith(PN); // Everyone use the PHI node now!
524  PN->addIncoming(&*I, NewEntry);
525  ArgumentPHIs.push_back(PN);
526  }
527 
528  // If the function doen't return void, create the RetPN and RetKnownPN PHI
529  // nodes to track our return value. We initialize RetPN with undef and
530  // RetKnownPN with false since we can't know our return value at function
531  // entry.
532  Type *RetType = F.getReturnType();
533  if (!RetType->isVoidTy()) {
534  Type *BoolType = Type::getInt1Ty(F.getContext());
535  RetPN = PHINode::Create(RetType, 2, "ret.tr", InsertPos);
536  RetKnownPN = PHINode::Create(BoolType, 2, "ret.known.tr", InsertPos);
537 
538  RetPN->addIncoming(UndefValue::get(RetType), NewEntry);
539  RetKnownPN->addIncoming(ConstantInt::getFalse(BoolType), NewEntry);
540  }
541 
542  // The entry block was changed from HeaderBB to NewEntry.
543  // The forward DominatorTree needs to be recalculated when the EntryBB is
544  // changed. In this corner-case we recalculate the entire tree.
545  DTU.recalculate(*NewEntry->getParent());
546 }
547 
548 void TailRecursionEliminator::insertAccumulator(Instruction *AccRecInstr) {
549  assert(!AccPN && "Trying to insert multiple accumulators");
550 
551  AccumulatorRecursionInstr = AccRecInstr;
552 
553  // Start by inserting a new PHI node for the accumulator.
554  pred_iterator PB = pred_begin(HeaderBB), PE = pred_end(HeaderBB);
555  AccPN = PHINode::Create(F.getReturnType(), std::distance(PB, PE) + 1,
556  "accumulator.tr", &HeaderBB->front());
557 
558  // Loop over all of the predecessors of the tail recursion block. For the
559  // real entry into the function we seed the PHI with the identity constant for
560  // the accumulation operation. For any other existing branches to this block
561  // (due to other tail recursions eliminated) the accumulator is not modified.
562  // Because we haven't added the branch in the current block to HeaderBB yet,
563  // it will not show up as a predecessor.
564  for (pred_iterator PI = PB; PI != PE; ++PI) {
565  BasicBlock *P = *PI;
566  if (P == &F.getEntryBlock()) {
568  AccRecInstr->getOpcode(), AccRecInstr->getType());
569  AccPN->addIncoming(Identity, P);
570  } else {
571  AccPN->addIncoming(AccPN, P);
572  }
573  }
574 
575  ++NumAccumAdded;
576 }
577 
578 // Creates a copy of contents of ByValue operand of the specified
579 // call instruction into the newly created temporarily variable.
580 void TailRecursionEliminator::copyByValueOperandIntoLocalTemp(CallInst *CI,
581  int OpndIdx) {
582  Type *AggTy = CI->getParamByValType(OpndIdx);
583  assert(AggTy);
584  const DataLayout &DL = F.getParent()->getDataLayout();
585 
586  // Get alignment of byVal operand.
587  Align Alignment(CI->getParamAlign(OpndIdx).valueOrOne());
588 
589  // Create alloca for temporarily byval operands.
590  // Put alloca into the entry block.
591  Value *NewAlloca = new AllocaInst(
592  AggTy, DL.getAllocaAddrSpace(), nullptr, Alignment,
593  CI->getArgOperand(OpndIdx)->getName(), &*F.getEntryBlock().begin());
594 
595  IRBuilder<> Builder(CI);
596  Value *Size = Builder.getInt64(DL.getTypeAllocSize(AggTy));
597 
598  // Copy data from byvalue operand into the temporarily variable.
599  Builder.CreateMemCpy(NewAlloca, /*DstAlign*/ Alignment,
600  CI->getArgOperand(OpndIdx),
601  /*SrcAlign*/ Alignment, Size);
602  CI->setArgOperand(OpndIdx, NewAlloca);
603 }
604 
605 // Creates a copy from temporarily variable(keeping value of ByVal argument)
606 // into the corresponding function argument location.
607 void TailRecursionEliminator::copyLocalTempOfByValueOperandIntoArguments(
608  CallInst *CI, int OpndIdx) {
609  Type *AggTy = CI->getParamByValType(OpndIdx);
610  assert(AggTy);
611  const DataLayout &DL = F.getParent()->getDataLayout();
612 
613  // Get alignment of byVal operand.
614  Align Alignment(CI->getParamAlign(OpndIdx).valueOrOne());
615 
616  IRBuilder<> Builder(CI);
617  Value *Size = Builder.getInt64(DL.getTypeAllocSize(AggTy));
618 
619  // Copy data from the temporarily variable into corresponding
620  // function argument location.
621  Builder.CreateMemCpy(F.getArg(OpndIdx), /*DstAlign*/ Alignment,
622  CI->getArgOperand(OpndIdx),
623  /*SrcAlign*/ Alignment, Size);
624 }
625 
626 bool TailRecursionEliminator::eliminateCall(CallInst *CI) {
627  ReturnInst *Ret = cast<ReturnInst>(CI->getParent()->getTerminator());
628 
629  // Ok, we found a potential tail call. We can currently only transform the
630  // tail call if all of the instructions between the call and the return are
631  // movable to above the call itself, leaving the call next to the return.
632  // Check that this is the case now.
633  Instruction *AccRecInstr = nullptr;
634  BasicBlock::iterator BBI(CI);
635  for (++BBI; &*BBI != Ret; ++BBI) {
636  if (canMoveAboveCall(&*BBI, CI, AA))
637  continue;
638 
639  // If we can't move the instruction above the call, it might be because it
640  // is an associative and commutative operation that could be transformed
641  // using accumulator recursion elimination. Check to see if this is the
642  // case, and if so, remember which instruction accumulates for later.
643  if (AccPN || !canTransformAccumulatorRecursion(&*BBI, CI))
644  return false; // We cannot eliminate the tail recursion!
645 
646  // Yes, this is accumulator recursion. Remember which instruction
647  // accumulates.
648  AccRecInstr = &*BBI;
649  }
650 
651  BasicBlock *BB = Ret->getParent();
652 
653  using namespace ore;
654  ORE->emit([&]() {
655  return OptimizationRemark(DEBUG_TYPE, "tailcall-recursion", CI)
656  << "transforming tail recursion into loop";
657  });
658 
659  // OK! We can transform this tail call. If this is the first one found,
660  // create the new entry block, allowing us to branch back to the old entry.
661  if (!HeaderBB)
662  createTailRecurseLoopHeader(CI);
663 
664  // Copy values of ByVal operands into local temporarily variables.
665  for (unsigned I = 0, E = CI->arg_size(); I != E; ++I) {
666  if (CI->isByValArgument(I))
667  copyByValueOperandIntoLocalTemp(CI, I);
668  }
669 
670  // Ok, now that we know we have a pseudo-entry block WITH all of the
671  // required PHI nodes, add entries into the PHI node for the actual
672  // parameters passed into the tail-recursive call.
673  for (unsigned I = 0, E = CI->arg_size(); I != E; ++I) {
674  if (CI->isByValArgument(I)) {
675  copyLocalTempOfByValueOperandIntoArguments(CI, I);
676  ArgumentPHIs[I]->addIncoming(F.getArg(I), BB);
677  } else
678  ArgumentPHIs[I]->addIncoming(CI->getArgOperand(I), BB);
679  }
680 
681  if (AccRecInstr) {
682  insertAccumulator(AccRecInstr);
683 
684  // Rewrite the accumulator recursion instruction so that it does not use
685  // the result of the call anymore, instead, use the PHI node we just
686  // inserted.
687  AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
688  }
689 
690  // Update our return value tracking
691  if (RetPN) {
692  if (Ret->getReturnValue() == CI || AccRecInstr) {
693  // Defer selecting a return value
694  RetPN->addIncoming(RetPN, BB);
695  RetKnownPN->addIncoming(RetKnownPN, BB);
696  } else {
697  // We found a return value we want to use, insert a select instruction to
698  // select it if we don't already know what our return value will be and
699  // store the result in our return value PHI node.
701  RetKnownPN, RetPN, Ret->getReturnValue(), "current.ret.tr", Ret);
702  RetSelects.push_back(SI);
703 
704  RetPN->addIncoming(SI, BB);
705  RetKnownPN->addIncoming(ConstantInt::getTrue(RetKnownPN->getType()), BB);
706  }
707 
708  if (AccPN)
709  AccPN->addIncoming(AccRecInstr ? AccRecInstr : AccPN, BB);
710  }
711 
712  // Now that all of the PHI nodes are in place, remove the call and
713  // ret instructions, replacing them with an unconditional branch.
714  BranchInst *NewBI = BranchInst::Create(HeaderBB, Ret);
715  NewBI->setDebugLoc(CI->getDebugLoc());
716 
717  BB->getInstList().erase(Ret); // Remove return.
718  BB->getInstList().erase(CI); // Remove call.
719  DTU.applyUpdates({{DominatorTree::Insert, BB, HeaderBB}});
720  ++NumEliminated;
721  return true;
722 }
723 
724 void TailRecursionEliminator::cleanupAndFinalize() {
725  // If we eliminated any tail recursions, it's possible that we inserted some
726  // silly PHI nodes which just merge an initial value (the incoming operand)
727  // with themselves. Check to see if we did and clean up our mess if so. This
728  // occurs when a function passes an argument straight through to its tail
729  // call.
730  for (PHINode *PN : ArgumentPHIs) {
731  // If the PHI Node is a dynamic constant, replace it with the value it is.
732  if (Value *PNV = SimplifyInstruction(PN, F.getParent()->getDataLayout())) {
733  PN->replaceAllUsesWith(PNV);
734  PN->eraseFromParent();
735  }
736  }
737 
738  if (RetPN) {
739  if (RetSelects.empty()) {
740  // If we didn't insert any select instructions, then we know we didn't
741  // store a return value and we can remove the PHI nodes we inserted.
742  RetPN->dropAllReferences();
743  RetPN->eraseFromParent();
744 
745  RetKnownPN->dropAllReferences();
746  RetKnownPN->eraseFromParent();
747 
748  if (AccPN) {
749  // We need to insert a copy of our accumulator instruction before any
750  // return in the function, and return its result instead.
751  Instruction *AccRecInstr = AccumulatorRecursionInstr;
752  for (BasicBlock &BB : F) {
753  ReturnInst *RI = dyn_cast<ReturnInst>(BB.getTerminator());
754  if (!RI)
755  continue;
756 
757  Instruction *AccRecInstrNew = AccRecInstr->clone();
758  AccRecInstrNew->setName("accumulator.ret.tr");
759  AccRecInstrNew->setOperand(AccRecInstr->getOperand(0) == AccPN,
760  RI->getOperand(0));
761  AccRecInstrNew->insertBefore(RI);
762  RI->setOperand(0, AccRecInstrNew);
763  }
764  }
765  } else {
766  // We need to insert a select instruction before any return left in the
767  // function to select our stored return value if we have one.
768  for (BasicBlock &BB : F) {
769  ReturnInst *RI = dyn_cast<ReturnInst>(BB.getTerminator());
770  if (!RI)
771  continue;
772 
774  RetKnownPN, RetPN, RI->getOperand(0), "current.ret.tr", RI);
775  RetSelects.push_back(SI);
776  RI->setOperand(0, SI);
777  }
778 
779  if (AccPN) {
780  // We need to insert a copy of our accumulator instruction before any
781  // of the selects we inserted, and select its result instead.
782  Instruction *AccRecInstr = AccumulatorRecursionInstr;
783  for (SelectInst *SI : RetSelects) {
784  Instruction *AccRecInstrNew = AccRecInstr->clone();
785  AccRecInstrNew->setName("accumulator.ret.tr");
786  AccRecInstrNew->setOperand(AccRecInstr->getOperand(0) == AccPN,
787  SI->getFalseValue());
788  AccRecInstrNew->insertBefore(SI);
789  SI->setFalseValue(AccRecInstrNew);
790  }
791  }
792  }
793  }
794 }
795 
796 bool TailRecursionEliminator::processBlock(BasicBlock &BB) {
797  Instruction *TI = BB.getTerminator();
798 
799  if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
800  if (BI->isConditional())
801  return false;
802 
803  BasicBlock *Succ = BI->getSuccessor(0);
804  ReturnInst *Ret = dyn_cast<ReturnInst>(Succ->getFirstNonPHIOrDbg(true));
805 
806  if (!Ret)
807  return false;
808 
809  CallInst *CI = findTRECandidate(&BB);
810 
811  if (!CI)
812  return false;
813 
814  LLVM_DEBUG(dbgs() << "FOLDING: " << *Succ
815  << "INTO UNCOND BRANCH PRED: " << BB);
816  FoldReturnIntoUncondBranch(Ret, Succ, &BB, &DTU);
817  ++NumRetDuped;
818 
819  // If all predecessors of Succ have been eliminated by
820  // FoldReturnIntoUncondBranch, delete it. It is important to empty it,
821  // because the ret instruction in there is still using a value which
822  // eliminateCall will attempt to remove. This block can only contain
823  // instructions that can't have uses, therefore it is safe to remove.
824  if (pred_empty(Succ))
825  DTU.deleteBB(Succ);
826 
827  eliminateCall(CI);
828  return true;
829  } else if (isa<ReturnInst>(TI)) {
830  CallInst *CI = findTRECandidate(&BB);
831 
832  if (CI)
833  return eliminateCall(CI);
834  }
835 
836  return false;
837 }
838 
839 bool TailRecursionEliminator::eliminate(Function &F,
840  const TargetTransformInfo *TTI,
841  AliasAnalysis *AA,
843  DomTreeUpdater &DTU) {
844  if (F.getFnAttribute("disable-tail-calls").getValueAsBool())
845  return false;
846 
847  bool MadeChange = false;
848  MadeChange |= markTails(F, ORE);
849 
850  // If this function is a varargs function, we won't be able to PHI the args
851  // right, so don't even try to convert it...
852  if (F.getFunctionType()->isVarArg())
853  return MadeChange;
854 
855  if (!canTRE(F))
856  return MadeChange;
857 
858  // Change any tail recursive calls to loops.
859  TailRecursionEliminator TRE(F, TTI, AA, ORE, DTU);
860 
861  for (BasicBlock &BB : F)
862  MadeChange |= TRE.processBlock(BB);
863 
864  TRE.cleanupAndFinalize();
865 
866  return MadeChange;
867 }
868 
869 namespace {
870 struct TailCallElim : public FunctionPass {
871  static char ID; // Pass identification, replacement for typeid
872  TailCallElim() : FunctionPass(ID) {
874  }
875 
876  void getAnalysisUsage(AnalysisUsage &AU) const override {
883  }
884 
885  bool runOnFunction(Function &F) override {
886  if (skipFunction(F))
887  return false;
888 
889  auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
890  auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
891  auto *PDTWP = getAnalysisIfAvailable<PostDominatorTreeWrapperPass>();
892  auto *PDT = PDTWP ? &PDTWP->getPostDomTree() : nullptr;
893  // There is no noticable performance difference here between Lazy and Eager
894  // UpdateStrategy based on some test results. It is feasible to switch the
895  // UpdateStrategy to Lazy if we find it profitable later.
897 
898  return TailRecursionEliminator::eliminate(
899  F, &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F),
900  &getAnalysis<AAResultsWrapperPass>().getAAResults(),
901  &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE(), DTU);
902  }
903 };
904 }
905 
906 char TailCallElim::ID = 0;
907 INITIALIZE_PASS_BEGIN(TailCallElim, "tailcallelim", "Tail Call Elimination",
908  false, false)
913 
914 // Public interface to the TailCallElimination pass
916  return new TailCallElim();
917 }
918 
921 
925  auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
927  // There is no noticable performance difference here between Lazy and Eager
928  // UpdateStrategy based on some test results. It is feasible to switch the
929  // UpdateStrategy to Lazy if we find it profitable later.
931  bool Changed = TailRecursionEliminator::eliminate(F, &TTI, &AA, &ORE, DTU);
932 
933  if (!Changed)
934  return PreservedAnalyses::all();
938  return PA;
939 }
llvm::Check::Size
@ Size
Definition: FileCheck.h:76
llvm::PreservedAnalyses
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:152
llvm::Argument
This class represents an incoming formal argument to a Function.
Definition: Argument.h:28
llvm::LLVMContext::OB_clang_arc_attachedcall
@ OB_clang_arc_attachedcall
Definition: LLVMContext.h:96
llvm::AAManager
A manager for alias analyses.
Definition: AliasAnalysis.h:1299
llvm::TargetIRAnalysis
Analysis pass providing the TargetTransformInfo.
Definition: TargetTransformInfo.h:2458
llvm::MemoryLocation::get
static MemoryLocation get(const LoadInst *LI)
Return a location with information about the memory reference by the given instruction.
Definition: MemoryLocation.cpp:35
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:17
llvm::createTailCallEliminationPass
FunctionPass * createTailCallEliminationPass()
Definition: TailRecursionElimination.cpp:915
llvm::Type::getInt1Ty
static IntegerType * getInt1Ty(LLVMContext &C)
Definition: Type.cpp:236
llvm::TailCallElimPass::run
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: TailRecursionElimination.cpp:919
llvm::CallInst::setTailCall
void setTailCall(bool IsTc=true)
Definition: Instructions.h:1681
llvm::ReturnInst
Return a value (possibly void), from a function.
Definition: Instructions.h:3017
llvm::DataLayout
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:113
llvm::BasicBlock::iterator
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:87
llvm::BasicBlock::getParent
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:104
IntrinsicInst.h
llvm::AnalysisManager::getResult
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:780
Scalar.h
InstIterator.h
Loads.h
llvm::Function
Definition: Function.h:60
P
This currently compiles esp xmm0 movsd esp eax eax esp ret We should use not the dag combiner This is because dagcombine2 needs to be able to see through the X86ISD::Wrapper which DAGCombine can t really do The code for turning x load into a single vector load is target independent and should be moved to the dag combiner The code for turning x load into a vector load can only handle a direct load from a global or a direct load from the stack It should be generalized to handle any load from P
Definition: README-SSE.txt:411
Pass.h
llvm::SmallVector
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1185
Statistic.h
llvm::TargetTransformInfo
This pass provides access to the codegen interfaces that are needed for IR-level transformations.
Definition: TargetTransformInfo.h:167
llvm::IRBuilder<>
TailRecursionElimination.h
DomTreeUpdater.h
ValueTracking.h
OptimizationRemarkEmitter.h
llvm::Instruction::insertBefore
void insertBefore(Instruction *InsertPos)
Insert an unlinked instruction into a basic block immediately before the specified instruction.
Definition: Instruction.cpp:83
GlobalsModRef.h
llvm::Type
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
Module.h
llvm::CallingConv::Tail
@ Tail
Tail - This calling convention attemps to make calls as fast as possible while guaranteeing that tail...
Definition: CallingConv.h:81
llvm::MaybeAlign::valueOrOne
Align valueOrOne() const
For convenience, returns a valid alignment or 1 if undefined.
Definition: Alignment.h:134
llvm::DominatorTreeBase< BasicBlock, false >::Insert
static constexpr UpdateKind Insert
Definition: GenericDomTree.h:242
llvm::FoldReturnIntoUncondBranch
ReturnInst * FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, BasicBlock *Pred, DomTreeUpdater *DTU=nullptr)
This method duplicates the specified return instruction into a predecessor which ends in an unconditi...
Definition: BasicBlockUtils.cpp:1315
llvm::SPII::Load
@ Load
Definition: SparcInstrInfo.h:32
llvm::SmallPtrSet
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:450
llvm::successors
auto successors(MachineBasicBlock *BB)
Definition: MachineSSAContext.h:29
llvm::CallBase::isByValArgument
bool isByValArgument(unsigned ArgNo) const
Determine whether this argument is passed by value.
Definition: InstrTypes.h:1678
llvm::MipsISD::Ret
@ Ret
Definition: MipsISelLowering.h:119
STLExtras.h
llvm::CallBase::arg_begin
User::op_iterator arg_begin()
Return the iterator pointing to the beginning of the argument list.
Definition: InstrTypes.h:1316
llvm::SmallVectorImpl::pop_back_val
LLVM_NODISCARD T pop_back_val()
Definition: SmallVector.h:654
LLVM_DEBUG
#define LLVM_DEBUG(X)
Definition: Debug.h:101
llvm::Instruction::mayHaveSideEffects
bool mayHaveSideEffects() const
Return true if the instruction may have side effects.
Definition: Instruction.cpp:695
F
#define F(x, y, z)
Definition: MD5.cpp:55
llvm::BasicBlock
LLVM Basic Block Representation.
Definition: BasicBlock.h:55
llvm::dbgs
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
llvm::initializeTailCallElimPass
void initializeTailCallElimPass(PassRegistry &)
Arg
amdgpu Simplify well known AMD library false FunctionCallee Value * Arg
Definition: AMDGPULibCalls.cpp:186
llvm::Instruction::getOpcode
unsigned getOpcode() const
Returns a member of one of the enums like Instruction::Add.
Definition: Instruction.h:157
llvm::all_of
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1605
llvm::SelectInst::Create
static SelectInst * Create(Value *C, Value *S1, Value *S2, const Twine &NameStr="", Instruction *InsertBefore=nullptr, Instruction *MDFrom=nullptr)
Definition: Instructions.h:1768
llvm::PassRegistry::getPassRegistry
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
Definition: PassRegistry.cpp:31
Constants.h
llvm::AAResults
Definition: AliasAnalysis.h:511
PostDominators.h
E
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
tailcallelim
tailcallelim
Definition: TailRecursionElimination.cpp:911
llvm::CallBase::getCalledFunction
Function * getCalledFunction() const
Returns the function called, or null if this is an indirect function invocation or the function signa...
Definition: InstrTypes.h:1396
llvm::BasicBlock::begin
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:297
llvm::PostDominatorTreeWrapperPass
Definition: PostDominators.h:73
llvm::AnalysisUsage
Represent the analysis usage information of a pass.
Definition: PassAnalysisSupport.h:47
false
Definition: StackSlotColoring.cpp:141
llvm::Instruction
Definition: Instruction.h:42
llvm::SPII::Store
@ Store
Definition: SparcInstrInfo.h:33
llvm::SimplifyInstruction
Value * SimplifyInstruction(Instruction *I, const SimplifyQuery &Q, OptimizationRemarkEmitter *ORE=nullptr)
See if we can compute a simplified version of this instruction.
Definition: InstructionSimplify.cpp:6465
llvm::DominatorTreeWrapperPass
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:302
llvm::STATISTIC
STATISTIC(NumFunctions, "Total number of functions")
llvm::Value::setName
void setName(const Twine &Name)
Change the name of the value.
Definition: Value.cpp:372
LoopDeletionResult::Modified
@ Modified
llvm::UndefValue::get
static UndefValue * get(Type *T)
Static factory methods - Return an 'undef' object of the specified type.
Definition: Constants.cpp:1769
llvm::DomTreeUpdater
Definition: DomTreeUpdater.h:28
llvm::CallBase::getParamByValType
Type * getParamByValType(unsigned ArgNo) const
Extract the byval type for a call or parameter.
Definition: InstrTypes.h:1751
llvm::LLVMContext::OB_ptrauth
@ OB_ptrauth
Definition: LLVMContext.h:97
SmallPtrSet.h
llvm::CallInst::isTailCall
bool isTailCall() const
Definition: Instructions.h:1668
llvm::Align
This struct is a compact representation of a valid (non-zero power of two) alignment.
Definition: Alignment.h:39
llvm::MCID::Call
@ Call
Definition: MCInstrDesc.h:155
llvm::isModSet
LLVM_NODISCARD bool isModSet(const ModRefInfo MRI)
Definition: AliasAnalysis.h:196
llvm::CallingConv::ID
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
llvm::CallBase::onlyReadsMemory
bool onlyReadsMemory(unsigned OpNo) const
Definition: InstrTypes.h:1720
INITIALIZE_PASS_END
#define INITIALIZE_PASS_END(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:58
CFG.h
PB
PassBuilder PB(Machine, PassOpts->PTO, None, &PIC)
firstNonDbg
static Instruction * firstNonDbg(BasicBlock::iterator I)
Definition: TailRecursionElimination.cpp:385
llvm::SPIRV::Decoration::Alignment
@ Alignment
llvm::instructions
inst_range instructions(Function *F)
Definition: InstIterator.h:133
llvm::Constant
This is an important base class in LLVM.
Definition: Constant.h:41
INITIALIZE_PASS_BEGIN
INITIALIZE_PASS_BEGIN(TailCallElim, "tailcallelim", "Tail Call Elimination", false, false) INITIALIZE_PASS_END(TailCallElim
llvm::Instruction::eraseFromParent
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:77
llvm::CallBase::doesNotAccessMemory
bool doesNotAccessMemory(unsigned OpNo) const
Definition: InstrTypes.h:1714
llvm::ConstantExpr::getBinOpIdentity
static Constant * getBinOpIdentity(unsigned Opcode, Type *Ty, bool AllowRHSConstant=false)
Return the identity constant for a binary opcode.
Definition: Constants.cpp:2837
llvm::TargetTransformInfoWrapperPass
Wrapper pass for TargetTransformInfo.
Definition: TargetTransformInfo.h:2514
llvm::PreservedAnalyses::preserve
void preserve()
Mark an analysis as preserved.
Definition: PassManager.h:173
INITIALIZE_PASS_DEPENDENCY
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
llvm::PHINode::addIncoming
void addIncoming(Value *V, BasicBlock *BB)
Add an incoming value to the end of the PHI list.
Definition: Instructions.h:2814
llvm::BranchInst::Create
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
Definition: Instructions.h:3155
llvm::DenseMap
Definition: DenseMap.h:716
I
#define I(x, y, z)
Definition: MD5.cpp:58
llvm::is_contained
bool is_contained(R &&Range, const E &Element)
Wrapper function around std::find to detect if an element exists in a container.
Definition: STLExtras.h:1670
llvm::Instruction::setDebugLoc
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
Definition: Instruction.h:364
IRBuilder.h
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
SI
StandardInstrumentations SI(Debug, VerifyEach)
llvm::OptimizationRemarkEmitter::emit
void emit(DiagnosticInfoOptimizationBase &OptDiag)
Output the remark via the diagnostic handler and to the optimization record file.
Definition: OptimizationRemarkEmitter.cpp:77
llvm::SelectInst
This class represents the LLVM 'select' instruction.
Definition: Instructions.h:1737
llvm::TTI
TargetTransformInfo TTI
Definition: TargetTransformInfo.h:162
llvm::Type::isVoidTy
bool isVoidTy() const
Return true if this is 'void'.
Definition: Type.h:139
llvm::TargetTransformInfo::isLoweredToCall
bool isLoweredToCall(const Function *F) const
Test whether calls to a function lower to actual program function calls.
Definition: TargetTransformInfo.cpp:279
canTransformAccumulatorRecursion
static bool canTransformAccumulatorRecursion(Instruction *I, CallInst *CI)
Definition: TailRecursionElimination.cpp:366
llvm::CallBase::arg_end
User::op_iterator arg_end()
Return the iterator pointing to the end of the argument list.
Definition: InstrTypes.h:1322
Builder
assume Assume Builder
Definition: AssumeBundleBuilder.cpp:651
llvm::User::setOperand
void setOperand(unsigned i, Value *Val)
Definition: User.h:174
llvm::Instruction::clone
Instruction * clone() const
Create a copy of 'this' instruction that is identical in all ways except the following:
Definition: Instruction.cpp:862
llvm::OptimizationRemarkEmitter
The optimization diagnostic interface.
Definition: OptimizationRemarkEmitter.h:33
llvm::CallBase::getParamAlign
MaybeAlign getParamAlign(unsigned ArgNo) const
Extract the alignment for a call or parameter (0=unknown).
Definition: InstrTypes.h:1742
DataLayout.h
llvm::Value::getType
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
llvm::AnalysisUsage::addPreserved
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
Definition: PassAnalysisSupport.h:98
llvm::Value::replaceAllUsesWith
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:529
llvm::BasicBlock::Create
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:97
llvm::CallInst::isNoTailCall
bool isNoTailCall() const
Definition: Instructions.h:1675
DL
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Definition: AArch64SLSHardening.cpp:76
llvm::DomTreeUpdater::UpdateStrategy::Eager
@ Eager
llvm::pred_empty
bool pred_empty(const BasicBlock *BB)
Definition: CFG.h:118
llvm::PredIterator
Definition: CFG.h:42
llvm::Value::getName
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:305
llvm::LoadInst
An instruction for reading from memory.
Definition: Instructions.h:176
llvm::CallBase::setArgOperand
void setArgOperand(unsigned i, Value *v)
Definition: InstrTypes.h:1346
llvm::ConstantInt::getFalse
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:874
llvm::CallBase::hasOperandBundlesOtherThan
bool hasOperandBundlesOtherThan(ArrayRef< uint32_t > IDs) const
Return true if this operand bundle user contains operand bundles with tags other than those specified...
Definition: InstrTypes.h:2114
llvm::MCID::Select
@ Select
Definition: MCInstrDesc.h:164
runOnFunction
static bool runOnFunction(Function &F, bool PostInlining)
Definition: EntryExitInstrumenter.cpp:69
markTails
static bool markTails(Function &F, OptimizationRemarkEmitter *ORE)
Definition: TailRecursionElimination.cpp:189
llvm::OptimizationRemarkEmitterWrapperPass
OptimizationRemarkEmitter legacy analysis pass.
Definition: OptimizationRemarkEmitter.h:146
llvm::ConstantInt::getTrue
static ConstantInt * getTrue(LLVMContext &Context)
Definition: Constants.cpp:867
llvm::PreservedAnalyses::all
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:158
llvm::PHINode::Create
static PHINode * Create(Type *Ty, unsigned NumReservedValues, const Twine &NameStr="", Instruction *InsertBefore=nullptr)
Constructors - NumReservedValues is a hint for the number of incoming edges that this phi node will h...
Definition: Instructions.h:2706
Elimination
Tail Call Elimination
Definition: TailRecursionElimination.cpp:911
llvm::CallBase::arg_size
unsigned arg_size() const
Definition: InstrTypes.h:1339
llvm::pred_end
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:112
llvm::AnalysisManager::getCachedResult
PassT::Result * getCachedResult(IRUnitT &IR) const
Get the cached result of an analysis pass for a given IR unit.
Definition: PassManager.h:799
DiagnosticInfo.h
Function.h
llvm::IntrinsicInst
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:46
AA
llvm::pred_begin
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:109
llvm::DominatorTreeAnalysis
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:267
llvm::OptimizationRemark
Diagnostic information for applied optimization remarks.
Definition: DiagnosticInfo.h:690
Instructions.h
llvm::Instruction::getDebugLoc
const DebugLoc & getDebugLoc() const
Return the debug location for this node as a DebugLoc.
Definition: Instruction.h:367
Dominators.h
llvm::CallBase::getArgOperand
Value * getArgOperand(unsigned i) const
Definition: InstrTypes.h:1341
DEBUG_TYPE
#define DEBUG_TYPE
Definition: TailRecursionElimination.cpp:84
llvm::AAResultsWrapperPass
A wrapper pass to provide the legacy pass manager access to a suitably prepared AAResults object.
Definition: AliasAnalysis.h:1347
llvm::Instruction::getParent
const BasicBlock * getParent() const
Definition: Instruction.h:91
InstructionSimplify.h
llvm::GlobalsAAWrapperPass
Legacy wrapper pass to provide the GlobalsAAResult object.
Definition: GlobalsModRef.h:148
TargetTransformInfo.h
llvm::BasicBlock::getFirstNonPHIOrDbg
const Instruction * getFirstNonPHIOrDbg(bool SkipPseudoOp=true) const
Returns a pointer to the first instruction in this block that is not a PHINode or a debug intrinsic,...
Definition: BasicBlock.cpp:216
llvm::PHINode
Definition: Instructions.h:2664
llvm::BasicBlock::getTerminator
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.h:119
llvm::CallBase
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1174
DerivedTypes.h
llvm::isSafeToLoadUnconditionally
bool isSafeToLoadUnconditionally(Value *V, Align Alignment, APInt &Size, const DataLayout &DL, Instruction *ScanFrom=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
Return true if we know that executing a load from this value cannot trap.
Definition: Loads.cpp:328
llvm::AnalysisManager
A container for analyses that lazily runs them and caches their results.
Definition: InstructionSimplify.h:42
canTRE
static bool canTRE(Function &F)
Scan the specified function for alloca instructions.
Definition: TailRecursionElimination.cpp:92
llvm::FunctionPass
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:308
llvm::CallInst
This class represents a function call, abstracting a target machine's calling convention.
Definition: Instructions.h:1474
BB
Common register allocation spilling lr str ldr sxth r3 ldr mla r4 can lr mov lr str ldr sxth r3 mla r4 and then merge mul and lr str ldr sxth r3 mla r4 It also increase the likelihood the store may become dead bb27 Successors according to LLVM BB
Definition: README.txt:39
llvm::PostDominatorTreeAnalysis
Analysis pass which computes a PostDominatorTree.
Definition: PostDominators.h:47
llvm::AnalysisUsage::addRequired
AnalysisUsage & addRequired()
Definition: PassAnalysisSupport.h:75
llvm::Value::takeName
void takeName(Value *V)
Transfer the name from V to this value.
Definition: Value.cpp:378
llvm::AllocaInst
an instruction to allocate memory on the stack
Definition: Instructions.h:58
llvm::User::getOperand
Value * getOperand(unsigned i) const
Definition: User.h:169
llvm::BranchInst
Conditional or Unconditional Branch instruction.
Definition: Instructions.h:3099
raw_ostream.h
BasicBlockUtils.h
InitializePasses.h
llvm::OptimizationRemarkEmitterAnalysis
Definition: OptimizationRemarkEmitter.h:164
llvm::Value
LLVM Value Representation.
Definition: Value.h:74
Debug.h
llvm::BranchInst::isConditional
bool isConditional() const
Definition: Instructions.h:3178
llvm::BranchInst::getSuccessor
BasicBlock * getSuccessor(unsigned i) const
Definition: Instructions.h:3192
llvm::CallBase::args
iterator_range< User::op_iterator > args()
Iteration adapter for range-for loops.
Definition: InstrTypes.h:1332
llvm::findAllocaForValue
AllocaInst * findAllocaForValue(Value *V, bool OffsetZero=false)
Returns unique alloca where the value comes from, or nullptr.
Definition: ValueTracking.cpp:4492
llvm::Use
A Use represents the edge between a Value definition and its users.
Definition: Use.h:43
llvm::SmallPtrSetImpl::insert
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:365
llvm::Intrinsic::ID
unsigned ID
Definition: TargetTransformInfo.h:37
canMoveAboveCall
static bool canMoveAboveCall(Instruction *I, CallInst *CI, AliasAnalysis *AA)
Return true if it is safe to move the specified instruction from after the call to before the call,...
Definition: TailRecursionElimination.cpp:329